The present invention relates generally to sequential circuits, and in particular to a flip-flop.
Flip-flops have many uses in today""s computers and digital circuits. Flip-flops are one of the most commonly used elements to implement sequential circuits, in which the primary output relies not only on the current values of the inputs, but also on the previous input values. A flip-flop is used to generate a steady state output signal having either a high (logical one) or a low (logical zero) potential.
A prior art flip-flop 100 is shown in FIG. 1. Flip-flop 100 receives a clock signal CK and a data signal D to produce signals Q and Q*. Signals CK and D provide inputs to the gates of a stack of series-connected transistors, which include p-channel transistors P1 and P2 and n-channel transistors N1 and N2. When the signal level of CK signal is low, P1 and N1 turn on, allowing signal D to propagate to node Y. Node Y connects to a transmission gate TG. When the signal level at CK signal is high, TG turns on, allowing the signal at node Y to pass to node L and subsequently become output signal Q and Q*.
One problem involved with flip-flop 100 is the speed of data signal D propagating to node Y when signal D is at a high level, because note Y has to be precharged through the series-connected transistors P1 and P2. Another problem associated with flip-flop 100 includes an issue of charge sharing, which occurs when transistor P1 and N1 are off. When P1 and N1 are off, if data signal D changes from a high level to a low level; this low level activates transistor P2, however, since P1 is off, the charge stored at node PP is shared by node Y. The charge sharing, sometimes, introduces inefficiency to the operation of flip-flop 100 by slowing it.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved flip-flop which can operate faster and has no charge sharing issue.